Iran’s supreme leader has blamed the Islamic Republic’s enemies for nationwide unrest, as authorities cracked down with increasing intensity on protesters, leading to the death toll rising.

“In the events of the past few days, the enemies of Iran are deploying every means at their disposal including money, arms and political and intelligence support to coordinate making troubles for the Islamic establishment,” Ayatollah Ali Khamenei said in his first public remarks since the protests began on Thursday.

Videos posted on social networks suggest riot police and protesters are becoming more confrontational. In a sign that the rhetoric is also hardening, Esmail Kowsari, a senior Revolutionary Guards commander, vowed that the elite forces would crush those he said were disturbing the country’s security. In the event that the unrest continued, “the authorities will undoubtedly make a decision and finish the business”, Kowsari said.

The US ambassador to the United Nations, Nikki Haley, called for international action in solidarity with the demonstrators and said the US would seek emergency UN sessions on Iran.

Haley, one of the most hawkish figures on Iran in the Trump administration, rejected Khamenei’s comments, saying the protests were “completely spontaneous”.

“By the thousands, Iranian citizens are taking to the streets to protest the oppression of their own government. It takes great bravery for the Iranian people to use the power of their voice, especially when their government has a long history of murdering its own people who dare to speak the truth,” Haley said. “We must not be silent,. The people of Iran are crying out for freedom.”

The US Department of State spokeswoman, Heather Nauert, later denied that the US was calling for regime change, saying it was simply backing the right of the protesters to demand changed policies from their government.

The demonstrations, the largest seen in Iran since its disputed 2009 presidential election, resumed on Tuesday evening for the sixth consecutive day.

The protests began on Thursday when opponents of Iran’s moderate president, Hassan Rouhani, gathered in north-eastern Iran to demonstrate over economic grievances. They then spread nationwide and took on more of an anti-regime dimension, including anti-Khamenei chants.

At least 21 people are now thought to have died across the country. More than 450 people have been arrested in Tehran alone since Saturday – nationwide figures have not been released.

The UN secretary general, Antonio Guterres, expressed his “regret” at the rising death toll and called on Tehran to respect the rights of peaceful protesters. “We expect that the rights to peaceful assembly and expression of the Iranian people will be respected,” his spokesman said.

The protests, stronger in the provinces than Tehran, appear dominated by members of the working class under 25 who have suffered the most in Iran’s sluggish economy.

Observers have said that the partial lifting of sanctions that followed Iran’s 2015 nuclear deal with the west delivered uneven economic benefits to the country. “Middle class fortunes have improved somewhat following the nuclear deal… on the contrary, members of the working class… [have been] very vulnerable,” said Esfandyar Batmanghelidj, the founder of the Europe-Iran business forum.

While the protests may have begun over economic grievances, they soon took on a political dimension. Chants have called on Ayatollah Ali Khamenei to step down and voiced opposition to Iran’s regional policy, including “Let go of Syria, think about us”.

Ali Shamkhani, the secretary of Iran’s supreme national security council, told a Lebanese Arabic-language TV channel that the number of messages on social networks sent online via Saudi Arabia showed the country was involved. He warned that Iran would retaliate with “an appropriate response” in due course.

In the first intervention of its kind, the actor Taraneh Alidoosti – famous for her collaboration with Iran’s Oscar-winning director Asghar Farhadi – called on Twitter for the authorities to refrain from using violence against protesters and instead to understand their anger and find a way to calm the situation.

A protest in Dorud on Monday.Photograph: AY-Collect/Sipa/Rex/Shutterstock

State TV and semi-official news agencies that used relatively conciliatory language last week are increasingly referring to the protesters as mobs who want to destroy public property. On Tuesday judicial authorities gave an ultimatum to protesters, threatening harsher sentences if the unrest continued.

State television said six protesters had been killed overnight as they tried to attack a police station in the town of Qahderijan in the central Isfahan region. It also said an 11-year-old boy and a 20-year-old man had been killed in the town of Khomeinishahr, while a member of Iran’s paramilitary militia was killed in the town of Najafabad. None of the reports could be confirmed independently.

Observers reported riot police riding on motorbikes and wielding batons on the streets of Tehran. Similar scenes were reported in other cities.

A Tehrani man who drives a taxi for Snapp, Iran’s equivalent of Uber, told the Guardian that motorbike-riding security guards with batons had been out in full force in Tehran on Monday night.

“I was out at 8 or 9pm and the atmosphere was tense. In Tehran the riot police was unleashed near Vanak Square, in Enghelab Street and in Naziabad,” he said. “I was in Vanak Square at 5pm and it was full of security guards.”

The driver said the protests were more widespread in the provinces than in Tehran because working class people in the provinces were the most affected by Iran’s economic problems. “In Kermanshah [in the west of Iran] there was an earthquake recently and a lot of those affected are still living outside,” he said. “In Ahwaz, 30 years after the [Iran-Iraq] war, the situation is still bad.

“The city of Arak has many industries and a lot of people are without jobs. One of my relatives works for a petrochemical company in Arak – they haven’t got salaries for a few months now, that’s why they’re out … Gradually people are getting fed up and raising their voice.”

Rouhani spoke with a number of parliamentarians on Monday in a meeting that officials insisted had been planned before the protests began. The president acknowledged anger over the country’s flagging economy, although he and others warned that the government would not hesitate to crack down on those it considered lawbreakers.

The Economist Intelligence Unit, a UK-based advisory business, said rising inflation and a recent increase in food prices were to blame for the protests, as well as a lack of economic development. Youth unemployment remained at about 40%, the EIU noted, despite a promise by the Rouhani administration that the 2015 nuclear deal would help to create jobs and improve people’s living standards.

The scale and speed at which the protests have spread across Iran have puzzled many in the country, including reformists who are critical of the political atmosphere but are wary of any move towards regime change.

Iran blocked access to social networks including Telegram and Instagram on Sunday but insisted the move was temporary. On Tuesday the US urged Iran to stop blocking social media and advised its citizens to set up virtual private networks, or VPNs, to circumvent censorship.

It’s hard to overstate the power of Telegram in Iran. Of its 80m population, an estimated 40m use the free app created by Russian national Pavel Durov. Its clients share videos and photos, subscribing to groups where everyone from politicians to poets broadcast to fellow users.

While authorities ban social media websites like Facebook and Twitter and censor others, Telegram users can say nearly anything. In the last presidential election, the app played a big role in motivating turnout and spreading political screeds.

Telegram touts itself as being highly encrypted and allows users to set their messages to “self-destruct” after a certain period, making it a favourite among activists and others concerned about their privacy. That too has made it a worry of Iranian authorities.

A channel run by an exiled journalist, Roohallah Zam, helped organise some of those who took to the street, including times and locations for protests, and was suspended by Durov after Iranian authorities complained that it was inciting violence.

Zam, who denies the allegations, responded by launching new channels to spread messages about upcoming protests before the government ordered the app shut down.

One of Iran’s most outspoken MPs, Mahmoud Sadeghi, said on Twitter he had urged the interior ministry not to link the protests with foreign powers, and instead to improve the economic situation, open up state television to diverse opinions and lift restrictions on regime critics.

In his latest tweet on the ongoing unrest, Donald Trump praised protesters for acting against Tehran’s “brutal and corrupt” regime. “The people have little food, big inflation and no human rights. The US is watching!” Trump wrote. Iran’s foreign ministry responded by saying the US president should focus on “homeless and hungry people” in his own country rather than insulting Iranians.

A spokeswoman for the EU foreign policy chief, Federica Mogherini, said the EU had been touch with authorities in Iran. “We expect that the right to peaceful demonstration and freedom of expression will be guaranteed,” she said.

Choosing one of the world’s most famous cartoon characters for a fake driving licence might seem like something only Homer Simpson himself would do, but this week police pulled over a driver who had done just that.

A unidentified male driver was stopped by police in Milton Keynes, Buckinghamshire, this week and presented the officer with the licence, featuring the character from The Simpsons.

The spoof licence came complete with an image of Simpson saying his “D’oh!” catchphrase, a signature and address. Thames Valley police said in a tweet: “The driver’s car was seized and he was reported for driving with no insurance and driving without a proper licence. D’oh!”

Donald Trump’s lawyers are seeking m in damages from Stephanie Clifford, the pornographic actor whose professional name is Stormy Daniels and who claims to have had an affair with the future president in 2006 and 2007.

A lawyer representing Trump attorney Michael Cohen’s company, Essential Consultants, claimed in federal court on Friday that Clifford had violated a non-disclosure agreement as many as 20 times.

Clifford has said she was secretly paid 0,000 to keep quiet. Cohen, who has said he was not reimbursed by the Trump Organization or the Trump campaign for making the payment, has not explained what the payment was for or whether Trump was aware of it.

According to Friday’s filing with the US district court for the central district of California, Cohen now plans to force the dispute from state to federal court and into closed-door arbitration.

Trump has also obtained a restraining order against Clifford.

Clifford’s counsel, Michael Avenatti, said the threat to pursue his client for millions and efforts to force the matter under the cover of anonymity amounted to bullying.

“To put it simply – they want to hide the truth from the American people. We will oppose this effort at every turn,” Avenatti said.

“The fact that a sitting president is pursuing over m in bogus ‘damages’ against a private citizen, who is only trying to tell the public what really happened, is truly remarkable. Likely unprecedented in our history. We are not going away and we will not be intimidated by these threats.”

The latest turn in the dispute trails what promises to be an explosive CBS 60 Minutes’ interview with Clifford, scheduled for broadcast next Sunday.

This week, Avenatti claimed six other women had similar stories to tell, two of whom were similarly under non-disclosure agreements. He also said Clifford had been threatened.

Avenatti has claimed the non-disclosure agreement signed by his client is invalid because Trump failed to sign it too. If the courts determine the NDA is valid, the actor could face a penalty of m for each violation.

The White House press secretary, Sarah Sanders, has rejected the notion that Trump approved the payment to Clifford. The White House has also denied Trump had an affair with Daniels.

Hours before a pedestrian bridge at Florida International University collapsed on Thursday, killing six people, engineers met the construction manager, state transportation officials and university representatives to discuss a crack on the structure.

The Miami-based university detailed the two-hour meeting in a statement released early on Saturday.

It said the session included a technical presentation by Figg Bridge Engineers that “concluded there were no safety concerns and the crack did not compromise the structural integrity of the bridge”.

The meeting ended at 11am. Three hours later, the bridge fell.

The Florida department of transportation (FDot) announced late on Friday that an engineer hired by the university left a voicemail message with the state agency two days before the collapse, seeking to draw attention to the crack.

In the call, which was not picked up until after collapse and has been released to the public, engineer W Denney Pate mentioned “some cracking that’s been observed on the north end” of the bridge but said he did not think it was a safety issue.

The state transportation department also said one of its consultants attended a meeting with the FIU bridge team hours before the collapse. It did not say the crack in the bridge had been discussed.

The National Transportation Safety Board chief investigator, Robert Accetta, said on Friday it was too soon to tell if cracks played a role in the bridge collapse.

“I would have to say that a crack in the bridge does not necessarily mean it’s unsafe,” he said.

University officials have said engineers had performed stress tests to determine the “resiliency of the concrete” in the bridge.

Late on Saturday police said that they believed they had recovered all the bodies of the victims of the collapse. Juan Perez, Miami-Dade police chief, told news media that they had recovered all five bodies of people in vehicles crushed under the bridge. A sixth person died at the hospital.

While police believed all victims had been accounted for, they nevertheless said the search and rescue was continuing.

One victim’s uncle raged against what he called the “complete incompetence” and “colossal failure” that allowed people to drive on the six-lane highway beneath the unfinished concrete span.

“Why they had to build this monstrosity in the first place to get children across the street?” said Joe Smitha, whose niece, Alexa Duran, was crushed. “Then they decided to stress test this bridge while traffic was running underneath it?”

Authorities have not released Duran’s name, but her family has said she died. The FIU freshman was studying political science.

In an emailed statement on Saturday night, the Florida International University president, Mark Rosenberg, said it would hold a moment’s silence for the victims at 1:47pm on Monday – the same time that the bridge went down.